It is narrated from Sayyiduna al-Nu'man bin Bashir (may Allah be pleased with him) that he (peace and blessings be upon him) said: "The example of the believers in their mutual love, kindness and compassion is that of a single body: when one limb of it suffers, the whole body becomes restless with sleeplessness and fever."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6430
Sayyidah Umm al-Darda' (may Allah be pleased with her) narrates: My master (husband) narrated to me that he heard the Messenger of Allah (peace and blessings be upon him) saying: "Whoever supplicates for his brother in his absence, the angel appointed (over him) says 'Amin' to it and says: 'O supplicant, and for you the same.'"
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الاستسقاء / 6431